Back to 'Unit 4: Dynamics'

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  • 4.5: Solving Problems Using Newton's Second Law: Weight

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    There are four common classical forces that will be discussed in the following sections: weight, normal force, tension, and friction. We will discuss each of these forces one at-a-time in each of the following sections.

    Weight refers to the force of gravity on an object of a given mass. Because it comes from gravity, the weight force is generally directed toward the earth. The equation that relates the mass of an object to its weight is F_{g}=mg . This equation works only on or near the surface of the Earth.

    Let's consider a coffee cup sitting on a table. The coffee cup is experiencing the force of its weight that draws it toward the center of the earth. This "pushes" down on the table. However, because of Newton's Third Law of Motion, there must be an equal magnitude force in the opposite direction also acting on this table to balance the forces.